This invention relates to providing major improvements to reflectors over present methods. These reflectors are used in Luminaires in the fields of area illumination for safety, recreation, residential and industrial needs. Benefits of this invention can also be applied to any field of applied optics using reflection where a controlled and consistent distribution of specularity is required. Below is a list of granted patents the inventor is familiar with and believes this invention is applicable to providing significant and consistent improvements to those patented inventions still active and of course to any new or like subsequent inventions.
U.S. PATENT DOCUMENTSU.S. Pat. No.Grant DateInventors5,586,015December 1996Baldwin, et al5,014,175May 1991Osteen, et al4,358,816November 1982Soileau4,303,971December 1981Hogue, et al4,280,170July 1981Baldwin4,254,456March 1981Grindle, et al4,186,433January 1980Baldwin3,975,936August 1976Baldwin, et al
The design challenge common to all reflector applications is to use each part of the reflector surface to intercept an amount of radiant energy from a source and reflect it through the reflector opening and directly to the area to be illuminated. That challenge is more easily met if the majority of the reflections are specular. But, with prior art, formed shapes, and the accompanying specular reflection required is seldom achieved.
One of the most disturbing factors resulting with prior art is that often discrepancies arise between the expected design results and the measured performance. Yet, it seems everything planned was done normally and nothing seemed to have gone awry.
However, it would be reasonable to assume that something physical in the overall reflector manufacturing, perhaps unknown, unsuspected or overlooked must be the cause of those occasions. That guiding question suggests a new review of all the existing prior art to identify any possible hidden or overlooked mechanical cause of those occasions. Therefore a short historical review of the technology and related background was done to identify any unknowns. This was done in two steps to better understand the prior art. First an “overview” was made of today's product manufacture and the apparent results. Secondly, a more “detailed” view and experimental observations of the reflection behavior of the presently formed surfaces with an attempt to find a means to quantify that refection behavior.
Overview: The earliest of Luminaires were made shortly after Thomas Edison invented the first incandescent light. Their objective was to use the lost upward light and return it to the workplace.
As improvements in lamps were developed, reflector designs evolved as did manufacturing technology with new forming methods. They began from wrapped flat circular or fluted surfaces into shallow cones. Later, stamped, or spun surfaces, some metal die cast and finally the present popular system of Hydro forming complex 3D shapes. For that, flat rolled Aluminum sheet evolved as the material of choice. It's high reflectivity in the visible spectrum, even higher in the IR, ductility that permits it to be stretched formed into the complex shapes, lightweight but with adequate strength and its low cost were the main factors.
For the last forty years, the expansion of the nation's roadway systems required volume production of roadway lighting fixtures. That was followed by similar growth results from outdoor and indoor applications. As the industry matured, the quantities of reflectors increased. So did the economic demand to use the source light more efficiently and for longer lifetimes.
As the overview above suggested, the following comments resulted primarily from a hands on feel and look of several reflector samples made under the present technology. One sample set were the raw formed parts, with flange trimmed and with holes punched for mounting the lamp socket. Another reflector was a fully formed and finished part with cleaning, brightening and an overcoat of a clear and inert surface added for protection. This overview examination yielded these typical observations.
The finished forms surfaces appeared smooth and continuous, inside and outside and appeared normal to the unaided eye. Also, to the unaided eye, the reflector's “exterior” surface appeared smooth even after the punching step. However, to the eye again, the reflector's exterior surface, appeared somewhat smoother (a qualitative term only) than the flange exterior and a bit brighter. In a form having facets, the facets appeared flat and even smoother. When formed curves are viewed carefully, their surfaces show the tool markings that generated the curvature. That obvious difference is perhaps more easily explained if one remembers a detail or two of the Hydro form process. In that process, a reflector blank sheet is stretched and wrapped around a steel tool to generate the reflector form. Controlled pressure is applied against the blank on the outside of the tool and comes through a flexible and conforming diaphragm with controllable pressure in the chamber behind it.
Occasionally near the reflector opening, a few bright small areas were observed. Upon closer examination, these small spots appeared to be drag marks rubbed onto the reflector surface resulting from removal of the formed reflector from that part of the tool. Though those drag marks appeared to the eye as brighter, a later test did not show them to be specular. The overview examination yielded little insight except that reflection behavior was still the suspected cause for the discrepancy between design and results as noted earlier. For a more detailed examination of the prior art, the full focus was centered on a deeper understanding of the reflecting surface. In fact, the search was for a physical replication of Snell's Law from these processed reflector materials.
Detailed Examination: This examination began with a search for a geometric definition or meaning of the terms involved. During this industry's long successful history, the term “Specularity” evolved as a commonly used qualitative term. It was often preceded by an equally non-illuminating term, “essentially”. It had many convenient connotations but seldom was an attempt noted to define specularity, or the lack of it, in a measurable and repeatable manner. One item common to all the above but mentioned only in the most obvious terms was the “reflecting surface”. It was often implied, suggested or defined to be essentially specular unless some particular application required the reflection to be diffuse. Clearly, a more detailed understanding of the surface was needed.
The priority for this test was to first prove the basic assumption that a specular surface would reflect a specular beam. To do that a short, square tool steel block, hardened to a minimum hardness of (Rockwell C-40), was ground, polished and buffed until it had a flat and mirror like surface on the upper side. Details of adjacent objects in daylight were clearly visible when imaged in the polished surface. When the tool was placed to intercept a fixed laser beam, the beam's reflected image appeared on the ceiling as a small bright spot and appeared the same as if the laser were pointed upward. When the specular laser beam was reflected to pass directly through the center of a translucent screen, the edges of the reflected laser beam appeared circular in cross section as did the beam. However, when the laser was reflected from any flat part of an unfinished production reflector, it was impossible to find the reflected beam on the ceiling.
That experiment confirmed the laser and the polished tool surface could demonstrate specularity. And, what appeared to the eye as a diffuse reflecting surface showed the total absence of any specularity. The setup so far, in principle, was acceptable and the model “Solid” was chosen as the appropriate geometry. The reason behind this choice is that the solid angle concept so realistically replicates the behavior of reflections of laser beams in actual testing and permits the opportunity to produce a measure of the order of magnitude as will be seen later.
The translucent screen, made from polar coordinate plotting paper, mounted in a cardboard frame was placed perpendicular to the reflected beam to intercept it about 9 inches away from the point of incidence. The pattern of polar plotting paper is a series of concentric circles of increasing radius with the inner one being ⅛ inch diameter. The concentric circular pattern was also divided by radial lines through the center. The screen frame was then adjusted until the laser's incident beam, reflecting off the specular tool. permitted the reflected specular-beam to pass directly through the center of the screen.
With the setup now having the capability to show total specularity, a mix of both, or the lack of it, the test setup was ready. The small production samples, mentioned above, were then placed to intercept the beam. The intent was to confirm and document that different degrees of specularity produced different reflection patterns on the screens geometry as they did. The results of the 3D setups and test surfaces are shown in four front views of four different reflection patterns. The individual different reflection surface setups are shown below in the FIGS. 1A-1D.
But, a question remained. It was the desire and need to check the differences in the screen pattern caused by the subsequent process of cleaning followed by chemical brightening. A just formed sample was washed with a mild soap and water, treated with a commercial Aluminum brightening chemical, ALUMIBRITE, (sold as an Acidic Cleaner Brightener) and then subjected to a laser beam reflectance test before and after. The brightening made the sample appear brighter to the eye but under the laser test, showed no gain in specularity. The preliminary conclusion of the laser beam experiments on parts from prior art manufacturing is that the residual specularity of the surfaces inside the reflector are the result of the extensive forming stresses which appear as relatively smooth to the eye and hand but at the dimensions of the wavelength of light in the visible spectrum, the surface appeared significantly deformed. At low magnification, 12.times. to 30.times., the surface looked like soft hilly terrain with relatively low altitude, wide base convex curves with random orientation and of relatively uniform size. When examined at higher magnifications (100.times. to 200.times.), the change from a flat sheet appeared much more significant. However when a laser beam was aimed at the surface, the reflected beam had spread so broadly, and apparently uniformly, it was impossible to tell where it went because neither, screen, ceiling or walls captured any visible beam fragments.
To confirm a possible cause for the surfaces disruption, six length measurements over the forms exterior were taken in a clockwise manner with 12 o'clock in line with the street side. Lengths across the flat flanges centered radially, then across and over corresponding angular paths of the formed part. These measurements showed stretch extensions several times beyond the material's elongation failure limit.
For example, the total stretch of the six blank diagonals to the formed lengths varied from 64% to 81% with an average linear stretch diagonally of 70%. Though the ultimate tensile strength was easily exceeded, the constraints of the tool, the possible use of an earlier reverse stretching, and the limited movement set by the forming diaphragm and the tool, all managed, with operator skill, to deliver a completely formed reflector having apparently adequate (and whole?) residual thickness. Actual thickness measurements of the removed samples show a typical reduction in original thickness, in the range of 5% to 25%, depending on the sample's position where removed. Metallurgical examination at magnifications of 100.times. or greater from edgewise cuts and encapsulated samples clearly showed a tortured multi-angled reflector surface.
Looking down at the reflecting surface from above, an observer could also see many depressions, folds, dents and small cavities. These observations substantiated the reason why much of the light energy as well as specularity is lost at each reflection from such a surface. Higher magnifications of the order of 300 .times., viewed with a binocular microscope showed the, as formed surface, as a rough graveled surface being littered with large rectangular blocks in random floating positions and some even partially submerged. They appeared to be crystal like in the uniformity of their shape, with the included angles of their sides, ends and surface of the blocks, all approximating 90 degrees.
In a search of patents of prior art related to reflectors for Luminaires, no references were found to claim the concept that a tailored reflection pattern on a tool could be used as a final mechanical process to control the proportion of Specular and Diffuse reflection. No references were made to using a mechanical method to press a tool against and into the reflector surface and set it as the final mechanical act to control specularity. Nor were any claims found to set the desired reflection properties just before chemical treatment so that any brightening treatment could be optimized to enhance specularity and reflectivity rather than possibly degrading the desired finish. And, lastly no references were found to suggest that solid angle geometry could help quantify the degree and repeatability of specularity.